Gas diffusion layer for fuel cell applications

ABSTRACT

A gas diffusion layer (GDL) for fuel cell applications that can prevented channels of a bipolar plate from being intruded. The gas diffusion layer is manufactured by cutting a GDL material at a certain angle such that a machine direction of the inherent high stiffness of the GDL material is not in parallel with a major flow field direction of a bipolar plate to prevent the GDL intrusion into the channels of the bipolar plate without modifying an existing method for manufacturing the gas diffusion layer. With the gas diffusion layer, the electrochemical performance of the fuel cell can be improved and manufacturing process can be improved even in the case where the width of the rolled GDL material is small.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. § 119(a) the benefit of KoreanPatent Application No. 10-2009-0119314 filed Dec. 3, 2009, the entirecontents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present disclosure relates to a gas diffusion layer (GDL) for fuelcell applications, which functions to discharge water as a product of anelectrochemical reaction in a fuel cell stack and transfer electrons.

(b) Background Art

In general, a polymer electrolyte membrane fuel cell (PEMFC) is used asa fuel cell for a vehicle. The PEMFC should be able to stably operateover a wide current density range such that it normally exhibits ahigh-power performance of at least several tens of kW under variousoperational conditions of the vehicle [S. Park, J. Lee, and B. N. Popov,J. Power Sources, 177, 457 (2008)].

The fuel cell generates electricity through an electrochemical reactionbetween hydrogen and oxygen. Hydrogen supplied to an anode as anoxidation electrode of the fuel cell is dissociated into hydrogen ionsand electrons. The hydrogen ions are transmitted to a cathode as areduction electrode through a polymer electrolyte membrane, and theelectrons are transmitted to the cathode through an external circuit. Atthe cathode, the hydrogen ions and electrons react with oxygencontaining air to generate electricity and heat and, at the same time,produce water as a reaction by-product.

When an appropriate amount of water produced during the electrochemicalreaction is present in the fuel cell, it performs the function ofmaintaining the humidity of a membrane electrode assembly (100).However, when an excessive amount of water is present and is notappropriately removed, a flooding phenomenon occurs at high currentdensity, and the flooding water prevents the reactant gases from beingefficiently supplied to the fuel cell, which results in an increase inthe voltage loss.

Here, the functions of the gas diffusion layer included in the fuel cellwill be described in more detail.

FIG. 1 is a schematic diagram showing the structure of a unit cellincluding gas diffusion layers.

The gas diffusion layer is attached to the outer surface of each ofcatalyst layers coated on both sides of a polymer electrolyte membraneof the unit cell for an oxidation electrode and a reduction electrode.The gas diffusion layers function to supply reactant gases such ashydrogen and air (oxygen), transfer electrons produced by theelectrochemical reaction, and discharge water produced by the reactionto minimize the flooding phenomenon in the fuel cell.

Typically, a commercially available gas diffusion layer has a dual layerstructure including a microporous layer (MPL) having a pore size of lessthan 1 μm when measured by mercury intrusion and a macroporous substrate(or backing) having a pore size of 1 to 300 μm [X. L. Wang, H. M. Zhang,J. L. Zhang, H. F. Xu, Z. Q. Tian, J. Chen, H. X. Zhong, Y. M. Liang, B.L. Yi, Electrochimica Acta, 51, 4909 (2006)].

The microporous layer of the gas diffusion layer is formed by mixingcarbon powder such as acetylene black carbon and black pearl carbon witha hydrophobic agent such as polytetrafluoroethylene (PTFE) and coatingthe mixture on one or both sides of the macroporous substrate.

Meanwhile, the macroporous substrate of the gas diffusion layer isgenerally composed of carbon fiber and a hydrophobic agent such as PTFEand may be formed of carbon fiber cloth, carbon fiber felt, or carbonfiber paper [S. Escribano, J. Blachot, J. Etheve, A. Morin, R. Mosdale,J. Power Sources, 156, 8 (2006); M. F. Mathias, J. Roth, J. Fleming, andW. Lehnert, Handbook of Fuel Cells-Fundamentals, Technology andApplications, Vol. 3, Ch. 42, John Wiley & Sons (2003)].

It is necessary to optimize the structural design of the gas diffusionlayer for fuel cell applications such that the gas diffusion layerprovides appropriate performance according to its application fields andoperational conditions. In general, in the formation of the gasdiffusion layer for fuel cell applications, the carbon fiber felt orcarbon fiber paper is preferred to the carbon fiber cloth since thecarbon fiber felt and carbon fiber paper have excellent properties suchas reactant gas supply properties, product water discharge properties,compression properties, and handling properties.

Moreover, the gas diffusion layer has a significant effect on theperformance of the fuel cell according to complex and various structuraldifferences such as the thickness, gas permeability, compressibility,degree of hydrophobicity, structure of carbon fiber, porosity/poredistribution, pore tortuosity, electrical resistance, and bendingstiffness. Especially, it is known that there is a significantdifference in the performance in the mass transport region (JapanesePatent No. 3331703 B2).

Recently, with the commercialization of the fuel cell, extensiveresearch and development for the mass production of the gas diffusionlayer as a core component of the fuel cell have continued to progress.The gas diffusion layer should provide excellent performance in the fuelcell and should have an appropriate level of stiffness to provideexcellent handling properties when several hundreds of cells areassembled in the fuel cell stack. When the stiffness of the gasdiffusion layer is very high in the roll direction of the GDL material,it is difficult to roll the GDL material for transport and storage, andthus the mass productivity is reduced. Moreover, according to theprevious reports, when the stiffness of the gas diffusion layer isinsufficient in the fuel cell, as shown in FIG. 2, the gas diffusionlayer may intrude into flow field channels of a bipolar plate (orseparator) during assembly of the fuel cell (which is called “GDLintrusion”) [Mao Nitta, Tero Hottinen, Olli Himanen, Mikko Mikkola, J.Power Sources, 171, 26 (2007); Yeh-Hung Lai, Pinkhas A. Rapaport,Chunxin Ji, Vinod Kumar, J. Power Sources, 184, 120 (2008); J. Kleemann,F. Finsterwalder, W. Tillmetz, J. Power Sources, 190, 92 (2009); M. F.Mathias, J. Roth, M. K. Budinski, U.S. Pat. No. 7,455,928 B2; T.Kawashima, T. Osumi, M. Teranishi, T. Sukawa, US 2008/0113243 A1].

When the GDL intrusion into the flow field channels of the bipolar plate(200) occurs, the space required for transferring reactant gases andproduct water is reduced, and the contact resistance between the gasdiffusion layer (106), the ribs or lands (204) of the bipolar plate, andthe polymer electrolyte membrane electrode assembly (100) is increased,which causes a significant deterioration in the fuel cell performance.

Since the GDL intrusion phenomenon is closely related with the flowfield structure of the bipolar plate, it is important to appropriatelydesign the flow field structure and increase the mechanical propertiesof the gas diffusion layer such as bending stiffness so as to achieveexcellent fuel cell performance.

Typically, the fuel cell bipolar plate is composed of a major flow fieldand a minor flow field, and it is necessary to prevent the gas diffusionlayer from intruding into the channels in the major flow fielddirection. For this purpose, it is important to increase the stiffnessof the gas diffusion layer oriented in the width (W) direction ratherthan the length (L) direction which is in parallel with the major flowfield direction of the bipolar plate. Otherwise, when the gas diffusionlayer having a low stiffness is oriented in the width direction of themajor flow field of the bipolar plate as shown in FIG. 2, the GDLintrusion into the major flow field of the bipolar plate is increased.

In order to solve this phenomenon, it is possible to use the inherentanisotropic properties of the gas diffusion layer.

That is, in the gas diffusion layer formed of carbon fiber felt orcarbon fiber paper as a support, a greater amount of carbon fibers isoriented in the machine direction during the formation, and thus the gasdiffusion layer in the machine direction has mechanical properties suchas bending stiffness, tensile stress, etc. higher than those in thecross-machine direction (CMD) or transverse direction (TD).

Therefore, it is typical that the machine direction of the rolled GDLmaterial is directed to the high stiffness direction and thecross-machine direction is directed to the low stiffness direction.

Conventionally, the gas diffusion layer is produced by intentionallyarranging carbon fibers having a greater length or diameter in thecross-machine direction through a specific process or by introducing ametal reinforcing material to increase the stiffness of the gasdiffusion layer in the width direction of the major flow field of thebipolar plate, thus preventing the gas diffusion layer from intrudinginto the channels (202) of the bipolar plate. Moreover, the gasdiffusion layer is produced by arranging carbon fibers having a smallerlength or diameter in the machine direction to facilitate the rolling ofthe GDL material to achieve the flexibility required for the rolling [M.F. Mathias, J. Roth, M. K. Budinski, U.S. Pat. No. 7,455,928 B2].

However, this method has problems that it is necessary to modify themethod by adding a complicated process to the typical method formanufacturing the gas diffusion layer and, especially, when a differentkind of metal reinforcing material is introduced, it may cause a varietyof problems such as poor miscibility with the gas diffusion layer,non-uniform quality, etc.

According to another prior art method for preventing the GDL intrusionusing anisotropic properties of carbon fiber woven cloth, the physicalproperties and handling properties of the cloth are insufficient, andthus it is difficult to use this method to manufacture the gas diffusionlayer for fuel cell applications. [T. Kawashima, T. Osumi, M. Teranishi,T. Sukawa, US 2008/0113243 A1].

Accordingly, the previously proposed methods for preventing the GDLintrusion into the flow field channels of the bipolar plate aregenerally disadvantageous in terms of mass productivity, which isrequired for the commercialization of fuel cell vehicles.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY OF THE DISCLOSURE

The present invention has been made in an effort to solve theabove-described problems associated with prior art. Accordingly, thepresent invention provides a gas diffusion layer (GDL) for fuel cellapplications, which is manufactured by optimizing a process of cutting aGDL material into a size that is suitable for a fuel cell stack withoutmodifying an existing method for manufacturing the gas diffusion layer.That is, the present invention provides a gas diffusion layer for fuelcell applications, which improves fuel cell performance by increasingthe stiffness of the gas diffusion layer in a width directionperpendicular to a major flow field direction of a bipolar plate bycutting a GDL material at a certain angle such that a machine directionof the inherent high stiffness of the GDL material is not in parallelwith the major flow field direction of the bipolar plate to prevent thegas diffusion layer from intruding into channels of the bipolar plate.

In one aspect, the present invention provides a gas diffusion layer(GDL) for fuel cell applications, the gas diffusion layer having a duallayer structure including a microporous layer and a macroporoussubstrate, in which the stiffness in a width direction perpendicular toa major flow field direction of a bipolar plate is increased by cuttinga rolled gas diffusion layer (GDL) material at a certain angle such thata machine direction of the inherent high stiffness of the GDL materialis not in parallel with the major flow field direction of the bipolarplate to prevent the gas diffusion layer from intruding into flow fieldchannels of the bipolar plate.

In a preferred embodiment, the gas diffusion layer may be manufacturedby cutting the GDL material at an angle in a range of 0° to 90°,preferably 25° to 90°, formed by the machine direction of the inherenthigh stiffness of the GDL material and the major flow field direction ofthe bipolar plate.

In another preferred embodiment, the rolled GDL material in the machinedirection may have a Taber bending stiffness in a range of 20 to 150g_(f)·cm, preferably 50 to 100 g_(f)·cm.

In still another preferred embodiment, the macroporous substrate whichconstitutes the gas diffusion layer may be formed of at least oneselected from the group consisting of carbon fiber felt and carbon fiberpaper.

In yet another preferred embodiment, the gas diffusion layer may have agas permeability of more than 0.5 cm³/(cm²·s), preferably 2.5cm³/(cm²·s).

Other aspects and preferred embodiments of the invention are discussedinfra.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, etc., and includes hybrid vehicles, electricvehicles, plug-in hybrid electric vehicles, hydrogen-powered vehiclesand other alternative fuel vehicles (e.g. fuels derived from resourcesother than petroleum). As referred to herein, a hybrid vehicle is avehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

The above and other features of the invention are discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present invention, and wherein:

FIG. 1 is a schematic diagram showing the structure of a unit cell;

FIG. 2 is a schematic diagram showing a gas diffusion layer, whichintrudes into major flow field channels of a bipolar plate bycompression of bipolar plate ribs during assembly of a fuel cell;

FIG. 3 is a diagram comparing a prior art method for manufacturing a gasdiffusion layer and a method for manufacturing a gas diffusion layer inaccordance with the present invention;

FIG. 4 is a schematic diagram showing the arrangement between a majorflow field direction of a bipolar plate and a high stiffness directionof a gas diffusion layer during cutting at different angles according toa method of the present invention, in which (a) shows a process ofcutting a rolled GDL material at different angles with respect to thehigh stiffness of the GDL material (cut at an angle of 0°) in a machinedirection and (b) shows the arrangement between the high stiffnessdirection of a new gas diffusion layer and the major flow fielddirection of the bipolar plate;

FIG. 5 is a schematic diagram comparing the structure of a prior art gasdiffusion layer (cut at an angle of 0°) and a gas diffusion layer (cutat an angle of 90°) of the present invention;

FIG. 6 is a schematic diagram showing a gas diffusion layer applied to afuel cell in accordance with the present invention;

FIG. 7 is a graph showing the electrochemical performances of 5-cellstacks (BP-1) having gas diffusion layers (GDL-1) cut at angles of 0°and 90°, in which (a) was measured at a relative humidity of 50%/50% and(b) was measured at a relative humidity of 100%/100%;

FIG. 8 is a graph showing the electrochemical performances ofsingle-cell stacks (BP-1) having gas diffusion layers (GDL-2) cut atangles of 0° and 90°, in which (a) was measured at a relative humidityof 50%150% and (b) was measured at a relative humidity of 100%/100%;

FIG. 9 is a graph showing the electrochemical performances (i.e.,current density at 0.6 V) of fuel cell stacks (BP-1) having a gasdiffusion layer (GDL-1) of the present invention and a gas diffusionlayer (GDL-2), which were cut at an angle of 90°, in which (a) wasmeasured at a relative humidity of 50%/50% and (b) was measured at arelative humidity of 100%/100%;

FIG. 10 is a graph showing the electrochemical performances of 5-cellstacks (BP-1) having gas diffusion layers (GDL-1) cut at angles of 0°,45°, 60°, and 90°, in which (a) was measured at a relative humidity of50%/50% and (b) was measured at a relative humidity of 100%/100%; and

FIG. 11 is a schematic diagram showing a method for manufacturing a gasdiffusion layer using a process of cutting a GDL material of the presentinvention when the width of a rolled GDL material is smaller than thesize of the gas diffusion layer, in which (a) shows a prior art methodand (b) shows the method of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variouspreferred features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent partsof the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Hereinafter reference will now be made in detail to various embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings and described below. While the invention will bedescribed in conjunction with exemplary embodiments, it will beunderstood that present description is not intended to limit theinvention to those exemplary embodiments. On the contrary, the inventionis intended to cover not only the exemplary embodiments, but alsovarious alternatives, modifications, equivalents and other embodiments,which may be included within the spirit and scope of the invention asdefined by the appended claims.

The present invention provides a gas diffusion layer for fuel cellapplications, which has a dual layer structure including a microporouslayer and a macroporous substrate and is prevented from intruding intoflow field channels of a bipolar plate, thereby providing excellentproperties such as reactant gas supply properties, product waterdischarge properties, electron transfer properties, etc.

In detail, the present invention provides a gas diffusion layer for fuelcell applications, which has a dual layer structure including amicroporous layer and a macroporous substrate, in which a GDL materialis cut at a certain angle such that a machine direction of the inherenthigh stiffness of a rolled GDL material is not in parallel with a majorflow field direction of a bipolar plate without modifying an existingmethod for manufacturing the gas diffusion layer, thereby preventing thegas diffusion layer from intruding into flow field channels of thebipolar plate.

The gas diffusion layer of the present invention is manufactured bycutting a GDL material at an angle in a range of 0° to 90°, preferably25° to 90°, formed by the machine direction of the inherent highstiffness of the GDL material and the major flow field direction of thebipolar plate. Here, the Taber bending stiffness of the rolled GDLmaterial in the machine direction (i.e., high stiffness direction) is ina range of 20 to 150 g_(f)·cm, preferably 50 to 100 g_(f)·cm. The reasonfor this is that if the Taber bending stiffness is less than 20g_(f)·cm, the stiffness is too small to be used as the gas diffusionlayer for fuel cell applications, whereas, if it is more than 150g_(f)·cm, the GDL material becomes too rigid, which makes it difficultto roll the GDL material, thereby reducing the mass productivity.

Moreover, the gas diffusion layer of the present invention has a gaspermeability of more than 0.5 cm³/(cm²·s), preferably 2.5 cm³/(cm²·s).The reason for this is that if the gas permeability is less than 0.5cm³/(cm²·s), the material transfer properties of the gas diffusion layeris significantly reduced.

Meanwhile, the macroporous substrate which constitutes the gas diffusionlayer may be formed of at least one selected from the group consistingof carbon fiber felt and carbon fiber paper.

EXAMPLES

The following examples illustrate the invention and are not intended tolimit the same.

In Examples 1 and 2 of the present invention, gas diffusion layers weremanufactured by cutting a GDL material produced by a prior art method ata certain angle to increase the stiffness of the gas diffusion layer inthe width (W) direction perpendicular to the major flow field directionof the bipolar plate as shown in FIG. 6.

Conventionally, the GDL material is cut such that the high stiffness ofthe GDL material in the machine direction is in the length (L) directionwhich is in parallel with the major flow field direction of the bipolarplate (cutting angle: 0°). However, in the present invention, the GDLmaterial was cut at an angle of 90° such that the high stiffness of theGDL material in the machine direction is in the width direction of themajor flow field of the bipolar plate, thereby increasing the stiffnessof the gas diffusion layer in the width direction of the major flowfield.

Two kinds of gas diffusion layers (GDL-1 and GDL-2) formed of carbonfiber felt were used in Examples 1 and 2 of the present invention, andtheir basic properties are shown in the following table 1.

TABLE 1 Physical Measurement properties conditions Units GDL-1 GDL-2Thickness 25 kPa μm 454 302 Taber Stiffness tester: g_(f) · cm MD: 65MD: 27 bending 150-E V-5* CMD: 11 CMD: 2 stiffness Measurement angle:15° Gas Gurley cm³/(cm² · s) 37 0.7 permeability *Taber Industries, USA

In Example 3 of the present invention, GDL-1 was cut at angles of 45°,60°, and 90° to compare the effect of improving the fuel cellperformance.

COMPARATIVE EXAMPLES

As shown in FIGS. 3 and 4, in Comparative Examples, the GDL material inthe machine direction was cut in the length (L) direction which is inparallel with the major flow field direction of the bipolar plate(cutting angle: 0°).

In order to evaluate the electrochemical performances of the gasdiffusion layers according to the Examples and Comparative Examples,various elements such as polymer electrolyte membranes, catalyst layers,connection devices, etc. were assembled and maintained in the same way.

Two kinds of bipolar plates (BP-1 and BP-2) having substantially thesame structure were used, in which BP-1 was used in Examples 1 and 2 andComparative Examples 1 and 2 and BP-2 was used in Example 3 andComparative Example 3.

Moreover, the electrochemical performances of the gas diffusion layersaccording to the Examples and Comparative Examples were evaluated bymeasuring and comparing cell potential-current density polarizationcharacteristics with respect to a single-cell stack or a 5-cell stackusing commercially available equipment.

The conditions during the measurement of the electrochemicalperformances of the fuel cell stacks having the gas diffusion layersaccording to the Examples and Comparative Examples were as follows:

-   -   Temperature at the inlet of the fuel cell stack: 65° C.;    -   Gas pressure: Near ambient pressure;    -   Relative humidity (RH) at the anode and cathode: 100%/100% or        50%/50%; and    -   Stoichiometric ratio (SR) at the anode and cathode: 1.5/2.0.

Under the above conditions, the evaluation of the electrochemicalperformances of the fuel cell stacks having the gas diffusion layersaccording to the Examples and Comparative Examples was performed in thefollowing manner.

At the relative humidity of 100%/100% or 50%/50%, the electrochemicalperformances of the gas diffusion layers according to Examples 1 and 2of the present invention and those of the gas diffusion layers accordingto Comparative Examples 1 and 2 were compared under standard operatingconditions, and the results are shown in FIGS. 7 and 8.

As shown in FIGS. 7 and 8, it can be seen that the electrochemicalperformances of the fuel cell stacks having the gas diffusion layers cutat an angle of 90° in accordance with the present invention were higherthan those of the fuel cell stacks having the gas diffusion layers cutat an angle of 0° in accordance with the prior art.

That is, in the case of GDL-1, as shown in FIG. 7, it can be seen thatat relative humidities of 50%/50% and 100%/100%, the current density ofthe gas diffusion layer cut at an angle of 90° according to Example 1 ofthe present invention measured at 0.6 V was increased about 12% and 15%,respectively, compared to the gas diffusion layer cut at an angle of 0°according to Comparative Example 1.

Moreover, in the case of GDL-2, as shown in FIG. 8, it can be seen thatat relative humidities of 50%/50% and 100%/100%, the current density ofthe gas diffusion layer cut at an angle of 90° according to Example 2 ofthe present invention measured at 0.6 V was increased about 18% and 16%,respectively, compared to the gas diffusion layer cut at an angle of 0°according to Comparative Example 2.

As shown in FIG. 6, without intending to limit theory, it is believedthat the reason for the improvement in the fuel cell performance is thatthe high stiffness direction of the gas diffusion layers wasappropriately oriented in the width (W) direction perpendicular to themajor flow field direction of the bipolar plate to prevent the GDLintrusion into the flow field channels of the bipolar plate.

The electrochemical performances (i.e., current density at 0.6 V) of thefuel cell stacks having the gas diffusion layers GDL-1 and GDL-2 (cut atan angle of 90°) according to Examples 1 and 2 of the present inventionwere compared, and the results are shown in FIG. 9. As shown in thefigure, it can be seen that the higher stiffness of the gas diffusionlayer contributes to the improvement in the fuel cell performance sincethe fuel cell performance of GDL-2 having a relatively low bendingstiffness was about 72% of the fuel cell performance of GDL-1 at allrelative humidities of 50%/50% and 100%/100%.

Moreover, the effect of the improvement in the fuel cell performance ofthe gas diffusion layers GDL-1 cut at angles of 0°, 45°, 60°, and 90°was evaluated, and the results are shown in FIG. 10. As shown in thefigure, it can be seen that the fuel cell performances of the gasdiffusion layers cut at angles of more than 45° were improved to a levelequivalent to that of the gas diffusion layer cut at an angle of 90° atall relative humidities of 50%/50% and 100%/100%.

Therefore, when the process of cutting the GDL material in accordancewith the present invention is employed, it is possible to easilymanufacture the gas diffusion layer with improved bending stiffnesswhich can prevent the GDL intrusion into the major flow field of thebipolar plate without modifying the existing method for manufacturingthe gas diffusion layer, thereby improving the fuel cell performance.

Especially, as shown in FIG. 11, when the width of the rolled GDLmaterial is small or when the length of the gas diffusion layer isrelatively large, it is difficult to manufacture the gas diffusion layerhaving a desired size with the prior art method; however, when themethod of the present invention is applied, it is possible to easilymanufacture the gas diffusion layer having a size suitable for thedesired use by cutting the GDL material at various angles (e.g., 45°,60°, etc.).

As described above, the present invention provides the followingeffects.

According to the present invention, it is possible to improve the fuelcell performance by changing the process of cutting the GDL material toincrease the bending stiffness of the gas diffusion layer, which isclosely related with the GDL intrusion into the flow field channels ofthe bipolar plate, without modifying the existing method formanufacturing the gas diffusion layer.

The invention has been described in detail with reference to preferredembodiments thereof. However, it will be appreciated by those skilled inthe art that changes may be made in these embodiments without departingfrom the principles and spirit of the invention, the scope of which isdefined in the appended claims and their equivalents.

What is claimed is:
 1. A fuel cell, comprising: a polymer electrolytemembrane having two side surfaces, wherein each side surface includes: acatalyst layer coated on the side surface of the polymer electrolytemembrane, a compressible gas diffusion layer (GDL) stacked on thecatalyst layer; and a bipolar plate on the compressible GDL andcomprises a major flow field and a minor flow field, wherein thecompressible GDL comprises a dual layer structure including amicroporous layer having a pore size of less than 1 μm when measured bymercury intrusion, the microporous layer composed of the mixture ofcarbon powder and a hydrophobic agent; and a macroporous substratehaving a pore size of 1 to 300 μm, the macroporous substrate composed ofcarbon fiber and a hydrophobic agent, and the compressible GDL has awidth direction perpendicular to a major flow field direction of thebipolar plate and a length direction which is in parallel with the majorflow field direction of the bipolar plate, and wherein the compressibleGDL is prepared by cutting a rolled GDL material at a certain angle in arange of 60°≤θ<90° with respect to a machine direction of the rolled GDLmaterial as determined by the major flow field direction of the bipolarplate, such that a high stiffness direction of the compressible GDL asthe machine direction of the rolled GDL material is not parallel withthe length direction of the compressible GDL, the machine direction ofthe rolled GDL material is the high stiffness direction of thecompressible GDL, wherein the high stiffness direction of thecompressible GDL as the machine direction of the rolled GDL material isarranged in one direction, the high stiffness direction of thecompressible GDL as the machine direction of the rolled GDL material isnot parallel with the length direction of the compressible GDL at anangle (θ) in a range of 60 °≤θ<90°, formed by the high stiffnessdirection of the compressible GDL and the length direction of thecompressible GDL and, at the same time, with the major flow fielddirection of the bipolar plate when the compressible GDL is stacked onthe bipolar plate to reduce intrusion of the compressible GDL into flowfield channels of the bipolar plate.
 2. A fuel cell, comprising: apolymer electrolyte membrane having two side surfaces, wherein each sidesurface includes: catalyst layers coated on the side surface of thepolymer electrolyte membrane, compressible gas diffusion layers (GDL)stacked on the catalyst layers; and bipolar plates on the compressibleGDL and comprises a major flow field and a minor flow field, wherein thecompressible GDL comprises a dual layer structure including amicroporous layer having a pore size of less than 1 μm when measured bymercury intrusion, the microporous layer composed of the mixture ofcarbon powder and a hydrophobic agent ; and a macroporous substratehaving a pore size of 1 to 300 μm, the macroporous substrate composed ofcarbon fiber and a hydrophobic agent, and the compressible the GDL has awidth direction perpendicular to a major flow field direction of thebipolar plate and a length direction which is in parallel with the majorflow field direction of the bipolar plate, and wherein the compressibleGDL is prepared by cutting a rolled GDL material at a certain angle in arange of 60°≤θ<90° with respect to a machine direction of the rolled GDLmaterial as determined by the major flow field direction of the bipolarplate, such that a high stiffness direction of the compressible GDL asthe machine direction of the rolled GDL material is not parallel withthe length direction of the compressible GDL, the machine direction ofthe rolled GDL material is the high stiffness direction of thecompressible GDL, wherein the high stiffness direction of thecompressible GDL as the machine direction of the rolled GDL material isarranged in one direction, the high stiffness direction of thecompressible GDL as the machine direction of the rolled GDL material isnot parallel with the length direction of the compressible GDL at anangle (θ) in a range of 60≤θ<90, formed by the high stiffness directionof the compressible GDL and the length direction of the compressibleGDL, and, at the same time, with the major flow field direction of thebipolar plate when the compressible GDL is stacked on the bipolar plateto reduce intrusion of the compressible GDL into flow field channels ofthe bipolar plate, wherein the rolled GDL material in the machinedirection has a Taber bending stiffness in a range of 20 to 150 g_(f)·cmprior to cutting.
 3. The fuel cell of claim 1, wherein the GDL has a gaspermeability of more than 0.5 cm³/(cm²·s).
 4. The fuel cell of claim 1,wherein the compressible GDL has a gas permeability of more than 2.5cm³/(cm²·s).
 5. A fuel cell comprising: a polymer electrolyte membranehaving two side surfaces, wherein each side surface includes: a catalystlayer coated on the side of the polymer electrolyte membrane; acompressible gas diffusion layer (GDL) attached to an outer surface ofthe catalyst layer; and a bipolar plate stacked to an outer surface ofthe compressible GDL wherein the bipolar plate is composed of a majorflow field and a minor flow field, wherein the major flow field islonger in length than the minor flow field, and the compressible GDL hasa width direction perpendicular to a major flow field direction of thebipolar plate and a length direction which is in parallel with the majorflow field direction of the bipolar plate, wherein the compressible GDLhas a dual layer structure including a microporous layer composed of themixture of carbon powder and a hydrophobic agent and a macroporoussubstrate composed of carbon fiber and a hydrophobic agent, and thebipolar plate is stacked on the macroporous substrate of the gasdiffusion layers, wherein the compressible GDL is prepared by cutting arolled GDL material at a certain angle with respect to a machinedirection of the rolled GDL material such that the machine direction ofthe GDL material is not parallel with the length direction of thecompressible GDL, the machine direction of the GDL material is a highstiffness direction of the compressible GDL, wherein the high stiffnessdirection of the compressible GDL as the machine direction of the rolledGDL material is arranged in one direction, the high stiffness directionof the compressible GDL is at an angle in a range of 60°≤θ<90° withrespect to the length direction of the compressible GDL such that thehigh stiffness direction of the compressible GDL as the machinedirection of the rolled GDL material is not parallel with the major flowfield direction of the bipolar plate when the compressible GDL isstacked on the bipolar plate to reduce intrusion of the compressible GDLinto flow field channels of the bipolar plate.
 6. The fuel cell of claim5, wherein each of the compressible GDLs has a gas permeability of morethan 0.5 cm³/(cm²·s).
 7. The fuel cell of claim 5, wherein each of thecompressible GDLs has a gas permeability of more than 2.5 cm³/(cm²·s).8. A fuel cell, comprising: a polymer electrolyte membrane having twoside surfaces, each side surface comprises: a catalyst layer coated oneach side surface of the polymer electrolyte membrane, a compressiblegas diffusion layer (GDL) stacked on each of the of the catalyst layer;and a bipolar plate stacked on each of the compressible GDL andcomprises a major flow field and a minor flow field, wherein thecompressible GDL comprises a dual layer structure including amicroporous layer having a pore size of less than 1 μm when measured bymercury intrusion, the microporous layer composed of the mixture ofcarbon powder and a hydrophobic agent; and a macroporous substratehaving a pore size of 1 to 300 μm, the macroporous substrate composed ofcarbon fiber and a hydrophobic agent, and the compressible GDL has awidth direction perpendicular to a major flow field direction of thebipolar plate and a length direction which is in parallel with the majorflow field direction of the bipolar plate, and wherein the compressibleGDL is prepared by cutting a rolled GDL material at a certain angle in arange of 60°≤θ<90° with respect to a machine direction of the rolled GDLmaterial as determined by the major flow field direction of the bipolarplate, such that a high stiffness direction of the compressible GDL asthe machine direction of the rolled GDL material is not parallel withthe length direction of the compressible GDL at an angle (θ) in a rangeof 60 °≤θ<90° , formed by the high stiffness direction of thecompressible GDL and the length direction of the compressible GDL, themachine direction of the rolled GDL material is the high stiffnessdirection of the compressible GDL, wherein the high stiffness directionof the compressible GDL as the machine direction of the rolled GDLmaterial is arranged in one direction, the high stiffness direction ofthe macroporous substrate of the compressible GDL as the machinedirection of the rolled GDL material is not parallel with the lengthdirection of the macrosubstrate substrate of the compressible GDL and,at the same time, with the major flow field direction of the bipolarplate when the compressible GDL is stacked on the bipolar plate toreduce intrusion of the compressible GDL into flow field channels of thebipolar plate.